The invention relates to a holographic optical component having at least one laser element, and a grating structure integrated on a carrier and acting as a holographic optical system, and to the use of such a component.
In the future, optical mass memories will replace more and more conventional magnetic systems such as magnetic disks or tapes for data storage purposes. The reading units required for these consist of a holographic optical component comprising various opto-electronic components such as laser diodes and detectors, and micro-optic components, such as lenses, beam expanders, and beam splitters, acting as the holographic optical system.
A holographic optical component used as a disk head is known from the publication "Lasermagazin", Vol. 5, 1985, page 75 "Integrated optics for reading optical disks", particularly from the illustration given on this page. Here, all components--a laser diode, four photodiodes, and a holographic optical system--are integrated on a monolithically integrated circuit. This chip comprises a waveguide layer arranged on a silicon substrate, and containing four photodiodes as the receiver, and the holographic optical system. The holographic optical system comprises a focussing diffraction grating for coupling the light beam of the laser diode, combined with a double grating structure used as the beam splitter. The laser diode is butt coupled to the silicon substrate. The focussing grating coupler guides the beam of the laser diode onto an optical disk by which the dispersed light reflected back is collected by the same grating and coupled into the waveguide layer. The double grating structure divides the light into two equal parts guided by the waveguide layer onto the two diode pairs so that focus and tracking can be checked. The circuit of 3.times.12 mm requires a large housing and restricts mobility. Coupling of the laser emission into the chip edge furthermore requires, after separated the wafer into chips, mechanical treatment of this edge which is very labour-intensive, and therefore not conductive to economical production. The construction of a holographic optical component of this type is a very complicated technology, and therefore very expensive and ill-suited for mass production.
In addition, a holographic optical component is known from EP-PS 0 123 048, where a laser diode and a photodetector are arranged on a substrate element. A coherent light beam of the laser passes through a first hologram and is deflected by the latter such that it impinges via a beam splitting hologram on a second focussing hologram, which deflects the beam and focusses it on a recording medium. The light beam reflected by the recording medium is again deflected through the second hologram, and separated by the beam splitting hologram from the light beam generated by the laser diode and deflected through a third hologram onto the detector. A drawback of this arrangement is in particular the use of four holograms that necessitates adjustments of each one.